A new Canadian report finds a direct connection between oil sand mining and elevated levels of cancer causing agents in regional water supplies.

The news is a blow for oil companies and the Canadian government, which rely on this method to tap the world's second largest oil reserve. It also hurts the case for the Keystone pipeline to link America to the sands.

I spent several days in Fort McMurray, and the expanse of mines surrounding the city, last year where residents said they understood mining held risks, but really just wanted some hard facts. Now, it looks like they've got them.

"I take my kids fishing to the lakes," one executive told me at the $270 million McDonald Island recreation park. "I don't let them swim in it, but I know some people do."

Probably not anymore, as the study found chemicals called PAHs up to 23 times higher than before oil sand mining. With production set to triple over the next 25 years, these levels will only go up and the study makes clear that the long-term effect on humans, and wildlife remains "unknown."